The present invention relates to water-jet propulsion systems for watercraft, and more particularly to a control system for effecting and controlling lateral movement of the craft.
The invention is particularly suitable for propulsion systems for hydrofoil craft, although its usefulness is not necessarily limited to such craft and it may be used in any water-jet propulsion system for watercraft of any type. Hydrofoil craft have a hull supported on struts which have foil systems at their lower ends. When such a craft is driven at sufficiently high speed, the submerged foils develop lift and support the hull above the water surface. Any suitable type of propulsion system can, of course, be used for these craft but water-jet propulsion systems are frequently used. In such a system, two jets are disposed on opposite sides of the center line of the craft. A water intake is provided in or on one of the struts which takes the water under ram pressure due to the forward movement of the craft through the water. Water entering through the intake divides into two streams and is directed to two pumps which accelerate the water and discharge it rearwardly in two high velocity jets, resulting in forwardlydirected reaction forces which propel the craft. A relatively simple system is thus provided which is capable of sustaining the desired high speed during foil-borne operation. At low speeds, such as when moving toward or away from a dock, the speed of the craft is such that the foils lose lift and the craft settles onto the water and operates in the hull-borne mode. The jet propulsion system functions in the same manner as at other times but at reduced speed of the pumps.
In normal operation, in either the foil-borne or hull-borne mode, the craft is steered by means of a helm which operates the rudder and control surfaces of the craft through a suitable control system. In addition, the two jets are used for sterring, at least in the hull-borne mode, either to assist the rudder and control surface action or as the primary steering means. For this purpose, the jets are provided with angularlymovable deflectors which control the direction of the jets. The deflectors are controlled from the helm in such a manner that the jets are maintained in parallel relation and can be simultaneously moved angularly to effect steering of the craft. In addition, a thrust reverser bucket is provided for each jet which can be moved into position to deflect the jet stream into a forward direction and thus reverse the direction of the thrust.
As mentioned above, when a hydrofoil or other craft is maneuvering to or away from a dock at the beginning or end of a trip, or in other similar situations, it operates in the hull-borne mode at relatively low speed. Lateral movement of the craft is frequently required under these conditions, with or without some amount of yaw, to bring the craft into the desired position. Yawing can be accomplished by reversing one of the jets but little lateral movement of the craft can be produced in this way. Bow thrusters have frequently been provided, therefore, for use during hull-borne maneuvering. Such a device consists of a propeller on a transverse shaft in the bow of the craft to provide lateral thrust. Such a bow thruster may be driven hydraulically from the main propulsion system, which limits the power available since maneuvering of this kind is usually done at idling speed or at relatively low speed, and the maximum diameter of a bow thruster propeller is limited by the relatively shallow draft of hydrofoil craft at the bow. The maximum thrust available for lateral maneuvering by means of a bow thruster is, therefore, quite limited. These devices provide a certain amount of low speed maneuvering ability but there are many conditions of wind velocity and direction, and of adverse currents, in which they have insufficient thrust, and in general the maneuverability obtainable by the use of bow thrusters is not satisfactory.